Pneumatically operated control system



May 19, 1953 A. w. GRlswoLD ET AL 2,638,911

PNEUMATICALLY OPERATED CONTROL SYSTEM Filed Dec. l, 1950 INVENTORSAUGUSTUS W. GRISWOLD NATHANIEL B. NICHOLS lllllllnn-:E

" RNEY May 19, 1953 A. w. GRlswoLD ET AL 2,638,911

PNEUMATICALLY OPERATED CONTROL SYSTEM Filed Dec. 1, 195o 2 sheets-sheet2 l I 16B v 16E mvENToRs.

AUGUSTUS M/.GRISWOLD /6G NATHAN/EL. B. NICHOLS A RNEY Patented May 19,195.3

PN EUMA'ICALTJY OPERATED CONTROL SYSTEM Augustus W. Griswold, Rochester,N. Y., and Nathaniel B. Nichols, St. Paul, Minn., assignors to TaylorInstrument Companies, Rochester, N. Y., a corporation of New YorkApplication December 1, 1950, Serial No. 198,696

l This invention relates to a pneumatically operated control system formaintaining the value of a variable such as temperature, pressure,liquid level, rate of flow and the like, at a given value.

The main feature of the present invention relates to a pneumaticallyoperated control sys- Ytern which insures prompt control action at thetime of start up of a given process operation and which affords improvedaccuracy in control and `yet utilizes apparatus which is less expensivethan much of the control apparatus now in use. Other features of theinvention will appear from the detailed description and claims whentaken with the drawings in which Fig. l is a diagrammatic showing of thepresent control system 4with several units thereof separated for ease indisclosures; Fig. 2 is a sectional View indicating how several of theunits of Fig. 1 can be combined into an integral commercial device; andFig. 3 is a fragmentary sectional view of one of the diaphragmstructures used in several of the units. e

Referring to the drawings there is illustrated,

`by way of example, a system for the control of temperature of a givenprocess P to which steam 'is supplied through the pipe 5 under thecontrol of a diaphragm motor valve 6, vthe valve G being controlled bythe system to admit the proper amount of steam into the process `tomaintain it at the desired temperature.`

The temperature of the process is sensed by a temperature transmitter 'Iincluding a capillary tube 8 of a tube system whichl terminates in abulb 9 exposed to the process medium. This transmitter may be similar inconstruction to that disclosed in the patent application of Matner etal., Serial No. '790,776 filed December 9, 1947, now Patent 2,536,198,granted January 2, 1951. The temperature transmitter I transmitsairunder pressure from the source II, at

va signal pressure proportional to the temperature value sensed at thebulb 9. This proportional pressure is communicated through the pipe I2to a primary unit A herein referred to as'the primary stage. The primaryunit is also in communication through pipe 3| and reducing valve 30 witha reference pressure at a set point or'control value with which thesignal pressure from the transmitter corresponds, whenkthe temperatureis at the control value. The primary stage is arranged to transmit anoutput pressure proportional to the deviation of the temperature fromthe control value and proportional to the rate of temperaturedeviationfrom thecontrol value. f

4 claims. (or. 137-84) The unit A comprise-s a casing formed of ajplurality of annular plates I3 together with a top cap I4 and a bottomcap I5. These plates and the caps together with diaphragms i6, I'I, andI8 provide a plurality of chambers I9, 20 and 2I. These diaphragmssealed at their margins and arranged vin parallel relation, are securedat their centers to a pillar 23. The lower end of this pillar carries abaie 24 which cooperates with an adjustably mounted nozzle 25 to varythe escape of compressed air therefrom. The lower end of the pillar 23is engaged by a spring 26, the compression of which can be adjusted by aset screwl 2l. The signal pressure transmitted through pipe I2, isintroduced into the chamber while the desired set point or controlpressure, the value of which is determined by the reducing valve 30, issupplied through the pipe 3| to the secondary chamber 2|. The pressurein primary chamber 20 supplied by the pipe I2 and the pressure in thesecondary-chamber 2| which is the set point pressure, are applied toopposite sides of the diaphragm I1 so that the difference in these twopressures is effective to move the pillar 23 and the baffle 24 up ordown depending upon whether the signal pressure or the set pointpressure is theV greater. A source of compressed air 32 is suppliedthrough the restriction 33 to the pipe 34. This pipe communicatesv withthenozzle 25 to providel a variable output pressure determined by therelation between the baffle 24 and the nozzle y25. The output pressurein pipe 34 cornmunicates with a secondary stage or unit B to bedescribed. This output pressure also communicates through the branchpipe 35 and the adjustable needle Valve B to the tertiary chamber I9,the pressure in chamber I9 tends to act in opposition to the differencein pressures in chambers 20 and 2|. The needle valve 36 and the capacityof the chamberl I 9, as well as a supplemental capacity (not shown) ifdesired, acts as` aI delaying means which provides a delayedproportional pressure change in chamber I9. Without this delay, asresults with valve 36 open wide so` that it offers .no resistance to theflow of air therethrough, the pressure in line 34 would be proportionalto the diiference between the signal pressure and the set pointpressure. With this delay means, the pressure in line 34 is alsoproportionalto the derivative or rate of change of the differencebetween the signal pressure and the set point pressure.

.v The unit B comprises a casing having a plurality of chambers definedin part by exible diaphragms. The casing comprises annular plates baiiie4l carried by the lower endv of the pillar 46, with respect to thenozzle 43. Compressed air from a suitable source, is supplied-throughthe restriction 49 to the nozzle 48.Y A sthe bafiie thus changes itsposition with respect to the nozzle 48, the output pressure in the pipe5): will vary accordingly. This pressure is applied to a unit C, knownas a booster relay'.

The booster relay comprises a casing including the top cap 5|,intermediate ring 52 and bottom capv 53 separated by diaphragms v54-and55 to denne the chambers 56, 51 and 58. The diaphragms are connected attheir centers by a pillar 59 so that they operate asa unit -againstthebiassing action of spring- SAP in response tothe difference in`pressuresappled tQtheir respective surfaces. The pillar59 has apassage-59a, therein leading to chamber 5l which communicates with theatmosphere through anpopeningi in ring 52. Pillar 59 has a Valve seat atthe entranceto the passage 58a, controlled by a ball valve 6,0 providedat the upper end of an upwardly spring-biassed valve stem 6| governingthe flow of air through the passage. Compressed air .fromV a rsuitablesource is supplied through the pipe |53l into chamber 58 under thecontrol of a ball valve 64 carried on the lower'end of the valve stem- 6I, and cooperating with a seat formedin the bottom cap at the entranceto chamber l58. The pressure Nin the chamber 58 is applied to thediaphragm55 tending to oppose the pressure applied tordiaphragm 54comprising a part of the chamber `56. Com.- pressed air is supplied fromthe chamber 58 through the pipe 65 which .communicates with is providedto compensate for load changes in the process. In the presentarrangement a branch '|2 of the pipe 55 communicates through the needlevalve with the chamber 13 of the reset unit D.v This chamber is definedby the casing of the unit D and by a flexible diaphragm 14. Thisdiaphragm cooperates with a nozzle 'l5 which leads lto the atmosphere.Compressed air from the source 16, is applied through the restrictiontothe chamber 'P8A at the upper side of the diaphragm 14. Thedifferential of the pressures in the chamber `'lf3-and '(8, moves thediaphragm 14 the diaphragm motor of valve 6, to position ,this

valve so that the proper .amount of steam is supplied through the pipe5, to correct any deviation from the desired value of the process. Thepipe 65 also communicates through the branch pipe -66 with a chamber 45in unit B to'effect a balance ff;

with the incoming pressure fromunit A which is supplied to the chamber43.

In order to adjust the sensitivityf the system, that is, the amount ofopeningof the valve 6 for any given temperature deviation in theprocess,

pneumatic adjusting means are provided. There is also combined with thismeans, a reset unit D which automatically compensates for load changesin the process being controlled.

The controlled pressure from the output ofthe booster relay, is appliedthrough. the pipe 65, needle valve 6l and pipe 68 to chamber 44 of unitB. A source of referencepre'ssure is also applied through the pipe 69and restriction 10 into the chamber 44. It will be understood that byopenwith-,respect to the nozzle l5 and thereby varies the' pressuresupplied through pipe 69 and the trolled pressure supplied through thebranch pipe '|12 to` the chamber 13. The needle valve 1| in pipe 'l2determines the rate at which the pressure changes in the chamber |3\ andtherebyl determines the reset time of the controller.

Preferably each of the nozzles 25 and 48 bleeds into a space atatmospheric pressure.

Each of the diaphragms have been shownl in Figs. 1 and 2 as formed of asingle sheet of flexible material reinforced-at each surface of itscentral portion by a reinforcing disc leaving an annular hinging portion'aty the inner wall of the casing. Actually certain of these diaphragms,notably diaphragme I6, 4|) and 4| are preferably composite diaphragms ofthe construction illustrated in Fig. 3. In this construction, thediaphragm comprises two sheets IBA and IBB of rubber or the like mountedin superimposed parallel relation in the wall of the casing where theirborders are sealed. The central areas of the two sheets are spaced bythe disc IEC and are reinforcedv by the clamping discs |6D and |6E. Thedisc |6C to,- gether with the inner wall of the casing `defines anannular space IBG which communicates With atmospheric pressure,- throughthe opening IGH. Since the space ISG is always at atmospheric pressurethe portions of the diaphragms 6A and ISB at the annular, space willalways bulge in the same directions as shown so that the control systemwill not be disturbed by a foreign response which would result if theseportions were to snap through to bulge outward to the positions whichare the reverse of thoseshown.

When the set. point pressure in chamber 2| and the transmitted signalpressure in chamber `Zliare equal, the equilibrium pressure in chamberI9v and in chamber 43 .is maintained by the compression of spring 26, atthe midspan position corresponding to a chosen intermediate value in therange between zero pressure and the pressure of lthis compressed airsource which may be twenty pounds per square inch. The secondary stageis adjusted so that when the pressures in chambers 45 and 44 are equal,the pressure in chamber43 is maintained at this same midhspan value bycompression of spring S. When pressure in chambers 44 and 45 are equal,no further reset action occurs on motor diaphragm valve 6, and thepressure in chamber 43 is at the same lmidspan value, determined byspring S.

In the operation of the system, let it be assumed that the temperatureat bulb 9, is stable at the control point, then the signal pressure inypipe l2 manuauy adjuscecieducingyaive (not shcwn).

However, in the present system automatic reset and reference lor setpoint pressure in pipe 3| are equal, at which time the pressures inchambers 20 and 2| are equal to each other and the pressure in chambersI6 and 43 are equal to each other. Then assume an increase in processtemperature at bulb 9 which actuates the transmitter 'I causlng it todeliver to the pipe I2 andl to chamber 2,0 a signal pressureproportional to the value, ofthe new temperature sensed at bulb 9.Thisincrease in pressure in chamber 20, since it is greaterthan thereference pressure in chamber 2|, tendsto move the pedestal 23 upwardthereby bringing baille 24 closer to the nozzle 25. This movement of thebaille with respect to the nozzle, changes the back pressure in pipe 34and branchipipe `35 leading to the chamber 43 of the secondary unit. Thepressure in pipe 35 is also applied through needle valve 36 to chamberI9. The action of chamber I9 operating through the baille 24.and nozzlemodifies-the pressure in pipe 35 so that the resulting pressure suppliedtofchamber43 is proportional to the value of temperature at bulb 9 andalso proportional to the rate of change of the temperature.

The increase inthe pressure in chamber 43 results in a downward movementof pillar 46 thereby bringing baille 41 closer to nozzle 48. Thisrelative movement of the baille and the nozzle results in a change inpressure in pipe 50 such that the pressure in chamber 56 of the boosterrelay, increases. This causes the pillar :59..to move downward tendingto vmove the ball 64 further from its seat with the result` that; air atincreased pressure is supplied throughthe booster relay to pipe 65leadingr to motor diaphragm valve 6. Valve 6 tends to close therebyreducing the amount of steam supplied to the-process.

The pressure in pipe 65 is also supplied through pipe 66 to chamber 45.tending to decrease .the nozzle-baffle displacement which resultsinpneumatic sensitivity reduction. Also the pressure in the pipe 65 issupplied through needle valve 61 and branch pipe 68 to the chamber 44.The pressure-change in` pipe 65 is applied through the adjustablerestriction or needle valve 61 which in combination with restriction 10`applies a fractional. part of pressure change in pipe 65 to chamber 44.This action causes pillar 46 to bring nozzle and baille into closerrelationship and removes part of the original sensitivity reduction. Itwill be understood that the time constant, associated with filling orpartially deflating chamber 44 is negligible.

In effectingreset action, lthe increase in the pressure in the pipe 65is applied through pipe 'i2 and needle Valve 1I, to chamber 13. `Theincreased ypressure in chamber 13, tends to move diaphragm 14 toward thenozzle 15, thereby tending to cap-off 'this nozzle 15 which action tendsto reduce the amount of air bleeding `therethrough to the atmospherewith a consequent increase in pressure in chamber 18. It will be notedthat' a source of huid ata reference pressure determined by a reducingvalve (not shown), is supplied through restriction 11 to the chamber 18.The action of the diaphragm I4 and nozzle 15 by tending to cap-oilnozzle 15 increases the pressure in chamber 18 and fluid at thispressure is supplied through pipe 69v and restriction 10 to the pipe 68in turn leading to chamber 44. 'The -action of the reset unit is suchthat the pressures in ythe chambers 13 and 18 have a one-to onerelation. The pressure change in pipe 65 in combination with restriction1| and the capacity of chamber 13 eiects a rate of change in thepressure supplied to pipe 69 and to chamber 44 of the secondary stage.This stage acts on the booster relay to eifect a rate of change ofpressure in pipe 65 which is applied to change the pressure applied tothe motor diaphragm valve ,6. Valve 6 tends to close thereby reducing,Jthe1 amount of heat supplied to the process. The further closing ofvalve 6 continues as long as the pressure in chambers 43 deviates fromthe predetermined mid-span value. y Pressure in chamber 43 will deviatefrom thismid-span value as long as the temperature atbulb 9 deviatesfrom the controlled point. A drop in temperature at the bulb 9 causesthe system to operate in a similar manner but in the opposite sense.

While the system has been described as controlling temperature, it isadapted to control other variables encountered in industry.

What we claim is: p

1. In a system for maintaining a variable condition at a givenhvalue,means for sensing the value of the condition, a primary unit portioncomprising casing walls and parallel diaphragms functioning therewith todefine primary, second-- ary and tertiary chambers, said primary chamberand said tertiary chamber acting in opposition to one another, anelement connecting said diaphragms to partake of the resultant movementthereof, means for applying to the primary chamber fluid under pressurecorresponding to the value of the variable condition, means forsupplying iiuid at a reference pressure to the secondary chamber, asource of iluid under pressure, an output pipe, valve means governed bythe resultan-t movement of said element for controlling the pressure ofsignal fluid supplied from said source to said output pipe, means forsupplying iiuid -to said tertiary chamber at a pressure related to thepressure of the signal fluid in said output pipe and at a rateproportional tothe rate of change of the pressure in said output pipe, asecondary unit portion comprising casing Walls and a group of paralleldiaphragms defining therewith a signal pressure chamber, a balancingpressure chamber, a reset chamber, certain of said last named 4group ofchambers acting in opposition to one another, a member connecting saiddiaphragms to partake of the resultant movement thereof, said signalchamber being responsive to the pressure of the signal fluid in saidoutput pipe, a control pipe, a primary source of fluid under pressure,means including valve mechanism governed by said member for controllingthe pressure ofoperating rluid suppliedV fromsaid primary source to saidcontrol pipe, means for supplying said operating'pressure iluid to saidbalancing chamber, 'a secondary source of fluid under pressure,meansresponsive to the operating fluid at the controlled pressure forcontrolling the pressure of the iluid from said secondary source, meansincluding a pressure proportioning network comprising'a pair ofrestrictions connected in mul-tiple, at least' one of whichis'adjustable and through which restrictions the operating pressureiluid and controlled pressure fluid from said secondary source arejointly supplied to vsaidreset chamber whereby the pressure of the fluidin the reset chamber is proportional both'to'the pressure of theoperating fluid and to the controlled pressure'of the secondary source,the proportionality factors being dependent on the ratio of theresistance values of said restrictions. l

2. In a system for maintaining a variable condition at a given value,means for sensing the value of the variable condition, a primary unitportion comprising casing'walls and parallel'diaphragms functioningtherewith to denne primary, secondary and tertiary chambers, 4saidVprimary chamber and Said tertiarrllamber. acting lili 0D- 7 positiontoene another, an element connecting said diaphragme to partake-of theresultant movement thereof, means for applying to the primary chamberfluid under pressure corresponding to the sensedY value of the' variablecondition, means for supplyingfuid at a given reference pressure to thesecondary chamber, a source-off fluid under pressure an output pipe,valve means governed by the resultant `movement of said element forcontrolling the pressure of signal fluid supplied from `said source tosaid output pipe, timel delay means for supplying fluid to said tertiarychamber at a pressure related to the pressure ofthe signalfluid :in saidoutput pipe, said time delay means including the capacity of saidtertiary chamber and a restriction `through which the fluid is suppliedto saidtertiary chamber, a secondary unit portion comprisingcasing wallsand a group of parallel diaphragme denning therewith a signal pressurechamber, a balancingfpressure chamber, a reset chamber, Certainofsaidlast named group of chambers actinglin cpposition'to one another, a,member connecting said diaphragms to partake of the resultant movementthereof,

said signal chamber Abeing responsive to the pres- Y sure of Athe signalfiuid in said output pipe, a primary source of lfluid under pressure, anoperating pressure pipe, means includingvalve mechanism governed by saidmember for controlling the pressure of operating fluid supplied fromsaid primary source lto said operating pressure pipe, means forsupplyingv said operating pressure to said balancing chamber, asecondary source of fluid under pressure, adjustable meansforcontrolling the pressure of the fluid from said sec- 1.

ondary source, and `means including a pressure proportloning networkcomprising a pair of restrictions connected in multiple through whichrestrictions the operating pressure uid and controlled pressure fluidfrom said secondary source are jointly supplied to said reset chamberwhereby the pressure of the fluid in the reset chamber is proportionalboth to the pressure of the operating iluidand to `the controlledpressure of the uid from thev secondarysource,y the proportionalityfactors being dependent on the ratio of the resistance values of saidrestrictions.

3. In a system for maintaining a variable condition ata given value,means for sensing the value of the variable condition, a primary unitportion comprising casing walls and parallel diaphragms functioningtherewith to define primary, secondary and tertiary chambers only,certain of which act in opposition to one another, an element connectingsaid diaphragms to partake of the resultant movement thereof, means forapplying to the primary chamber fluid under pressure corresponding tothe sensed value of the variable, means for supplying fluid at a givenreference pressure to the secondary chamber. a source of fluid underpressure, an output pipe, valve means governed by the resultant movementof said `element for controlling the pressure of signal fluid suppliedfrom said source to said output pipe, means for supplying fluid to saidtertiary chamber at a pressure related to the pressure of the signalfluid in said output pipe, a secondary unit portion comprising casingwalls and a group of parallel diaphragme defining therewith a signalpressure chamber, a balancing pressure chamber, a reset chamber, certainof said last named group of chambers acting in opposition to oneanother, a member connecting said diaphragme to partake of the resultant'movement thereof,-said signal chamber being-rewie 8 sponsi've to thepressure ofthe signal'fluidfin said outputpipe, aprimary source of fluidunder pressure,` anoperating pressure pipe,- means including valvemechanism` governed `by said member for controlling the pressure ofoperatingfluid supplied from said primary source lto'said operating.pressure pipe, means for supplying said operating pressure fluid tosaid balancing chamber, la secondary source of fluid under pressure,automatic reset adjusting means responsive to the operating fluid. ofthe 4controlled pressure for. controlling the pressure of the fluid fromsaidv secondary source, selectively 'adjustable means for varying therate of rresponse of said reset adjusting means, means including vapressure proportioning network comprising a pair of restrictionsconnected in multiple through which restrictions the operating pressurefluid and controlled pressure fluid from said secondary source arejointly supplied to said reset chamber Whereby the pressure of the fluidinthe reset chamber is proportional both tothe pressure of the operatingfluid and to the controlled pressure of the secondary source, theproportionality factors being dependent on the ratio of the resistancevalues of said restrictions.

4. In a system for maintaining a variable-condition at a given value,means for sensing the value of the condition, a primary unit portioncomprising ycasing walls and parallel diaphragms functioning therewithto define primary, secondary and tertiary chambers certain of `which actin opposition to one another, an element connecting Asaid diaphragm topartake of the resultant movement thereof, means for applying totheprimary chamber fluid under pressure corresponding to the value of thevariable condition, means for supplying fluid at a given referencepressure to the secondary chamber, a source of fluid under pressure, anoutputpipe, valve means governed by the resultant movement ofsaidelement for controlling the pressure of signal uid supplied fromsaid source to said output pipe, means for supplying fluid to saidtertiary chamber at a pressure related to the pressure of the signalfluid in said output pipe and at a rate proportional to the rate ofchange of the pressure-in said output pipe, a secondary `unit portioncomprising casing walls and a group .of parallel diaphragme definingtherewith a signal pressure chamber, a balancing pressure chamber, areset chamber, certain of said last named group of chambers acting inopposition to one another, a member connecting said diaphragms topartakeof the resultant movement thereof, said signal chamber being responsiveto the pressure of the signal fluid insaid output pipe, a control pipe,a primary source of fiuid under pressure, means including valvemechanism governed by said member for controlling the pressure ofoperating fluid supplied from said primary source to said control pipe,means for supplying said operating pressure fluid to saidbalancingchamber, a secondary source of fluid under pressure, meansresponsive to the voperating fluid at the controlled pressure forcontrolling the pressure `of the fluid from said secondary source, meansincluding a pressure proportioning network comprising a pair ofrestrictions connected in multiple, at least one of which is adjustableand through which restrictions the operating Ypressure fluid andcontrolled pressure fluid from said secondary source are jointlysupplied to said reset chamber whereby the pressure of the fluid in theresetv chamber is proportional both to the 10 pressure of the operatingfluid and to the con- Number Name Date trolled pressure of the secondarysource, the pro- 2,441,405 Fitch May 11, 1940 portionality factors beingdependent on the ratio 2,517,051 Swenson Aug. 1, 1950 of the resistancevalues of said restrictions, and 2,520,468 Moore Aug. 29, '1950 meanstending to bias said member to a selected 5 midspan position. FOREIGNPATENTS AUGUSTUS W. GRIsWoLD. Number Country Date NATHANIEL B,NICI-101,5l 544,643 Great Britain Apr. 22, 1942 544,753 Great BritainVApr. 27, 1942 References in the le 0f partent' 1o UNITED STATES PATENTSMoore Products Co., Philadelphia, Pa., Instruc- Number Name Date tions505-8 for Nullmatic Controller, 1948, pages 1,371,243 Hopwood Mar. '15,1921 2-7.

